mig-14 is a horizontally acquired, host-induced gene required for Salmonella enterica lethal infection in the murine model of typhoid fever

We have characterized a host-induced virulence gene, mig-ii, that is requir ed for fatal infection in the mouse model of enteric fever. mig-14 is prese nt in all Salmonella enterica subspecies I serovars and maps to a region of the chromosome that appears to have been acquired by horizontal transmissi on. a mig-ii mutant replicated in host tissues early after infection but wa s later cleared from the spleens and livers of infected animals. Bacterial clearance by the host occurred concomitantly with an increase in gamma inte rferon levels and recruitment of macrophages, but few neutrophils, to the i nfection foci. We hypothesize that the mig-14 gene product may repress immu ne system functions by interfering with normal cytokine expression in respo nse to bacterial infections.